What is called diesel combustion, in which fuel is directly injected into compressed air in the combustion chamber, self-ignites, and is burned by diffusion combustion, has a higher thermal efficiency as compared to combustion by spark ignition. In recent years, in order to enjoy this advantage of diesel combustion also in gasoline engines, technology for causing gasoline to self-ignite and burn by diffusion combustion has been developed.
PTL 1 discloses a technology enabling diesel combustion using as fuel natural gas or the like having a relatively high self-ignition temperature. According to PTL 1 disclosing this technology, fuel injection is performed in a predetermined spark-ignition region in the combustion chamber in an early or middle stage of the compression stroke to form air-fuel mixture that can be spark-ignited. Then, the air-fuel mixture formed in the spark-ignition region is ignited at a time immediately before the top dead center of the compression stroke to bring about combustion by spark ignition. Thus, a high-temperature, high-pressure condition enabling self-ignition of natural gas is established in the combustion chamber. Thereafter, fuel is injected directly into the combustion chamber in a high-temperature, high-pressure condition, so that the injected fuel is burned by diesel combustion.
It is well known to provide what is called an EGR apparatus in the internal combustion engine that performs diesel combustion. The EGR apparatus supplies a portion of exhaust gas flowing in the exhaust passage into the intake passage as EGR gas in order to reduce the amount of NOx generated. In the internal combustion engine equipped with such an EGR apparatus, when the EGR rate (the proportion of the quantity of the EGR gas in the intake air) is changed in response to a change in the operation state of the internal combustion engine, there is a delay in the change in the EGR rate from the change in the fuel injection quantity. If the EGR rate deviates from a range suitable for the operation state of the internal combustion engine due to this response delay in the EGR rate, there is a possibility that the torque of the internal combustion engine and/or the combustion noise cannot meet the requirements. PTL 2 discloses a technology that solves this problem in internal combustion engines in which EGR gas is supplied into the intake passage. In this technology, fuel injection parameters such as the injection time of main fuel injection performed at a time near the top dead center of the compression stroke, the injection quantity in sub-fuel injection performed prior to the main fuel injection, and/or the interval between the sub-fuel injection and the main fuel injection are corrected using a predetermined correction gain, during transient operation.
PTL 3 discloses a technology applied to an internal combustion engine having a plurality of cylinders. In this technology, during transient operation, a combustion parameter for each of the cylinders is controlled based on the distance from the EGR valve to the cylinder along the flow path of the EGR gas.